Solar cell module having a surface coating material of three-layered structure

ABSTRACT

A solar cell module comprising a photovoltaic element (solar cell) enclosed by a filler material and a coating material having a three-layered structure which is disposed on the light receiving side of the photovoltaic element, wherein said coating element includes a hard resin layer having a hardness of at least 50 in Shore hardness D; and adhesive layer having the functions of absorbing ultraviolet rays of wavelengths which deteriorate said hard resin layer and of transmitting ultraviolet rays necessary for electrical power generation by the photovoltaic element, and also having an adhesive function; and an outermost layer of excellent weatherability (the resin itself having excellent stability against heat, light, and moisture, the hard resin layer, adhesive layer, and outermost layer being laminated in this order on the filler material covering the light receiving surface of the photovoltaic element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solar cell module which excels inweatherability, heat resistance, moisture resistance, scratchresistance, and has an excellent protective ability against externalpressure. More particularly, the present invention relates to a solarcell module comprising a photovoltaic element (that is, a solar cell)enclosed by a filler material and a coating material having athree-layered structure which is disposed on the light receiving surfaceof the solar cell, wherein said coating material is composed of a layermade of hard resin having a hardness of 50 or more in Shore hardness D(hereinafter, referred to as a hard resin layer); a layer having afunction of absorbing ultraviolet rays liable to deteriorate the hardresin layer and capable of transmitting light necessary forphotoelectric conversion of the solar cell and also having an adhesivefunction (hereinafter, referred to as an adhesive layer); and a layermade of a resin excellent in weatherability (the resin itself beingstable against heat, light, and moisture; hereinafter, referred to as anoutermost layer), said hard resin layer, adhesive layer, and outermostlayer being laminated on the light receiving surface side of thephotovoltaic element in this order from the light receiving surfaceside. The coating material having the above-described three-layeredstructure in the solar cell module of the present invention preventsdamage to the photovoltaic element when applied with external pressure,and provides the weatherability, heat resistance, moisture resistance,and scratch resistance necessary for the solar cell module.

2. Related Background Art

Recently, a number of thin film solar cells have been proposed. Atypical one of these thin film solar cells is an amorphous silicon(a-Si) thin film solar cell. As for the a-Si thin film solar cell, thereis known a type in which an a-Si semiconductor film functioning as aphotoelectric conversion element is provided on a conductive substrateand a transparent conductive layer is provided on the semiconductor thinfilm. In the case where the a-Si thin film solar cell having the aboveconstruction is used as a power supply means, the surface of the a-Sisolar cell on the light incident side must be protected, unlike a solarcell having a construction using a glass sheet as the substrate. Forthis purpose, a protective means is provided on the surface of the a-Sisolar cell on the light incident side. It is most important for theprotective means to sufficiently transmit sunlight in order to maintainthe conversion efficiency of the solar cell. The protective means isalso required to protect the interior of the solar cell against wind andrain and the other external influences (hereinafter, referred to asinterior protective ability). It is also important that the protectivemeans itself be prevented from being deteriorated, discolored, andreduced in mechanical strength due to light, heat, and moisture. As sucha protective means, there is known a type in which a transparent resinlayer of excellent weatherability is provided on the light receivingsurface side as a surface coating layer, and a filler material made ofthermoplastic transparent resin is provided below the transparent resinlayer. The resin layer as the surface coating layer is generallycomposed of an acrylic resin film or a fluororesin film such as atetrafluoroethylene-ethylene copolymer film or polyvinyl fluoride film.As described above, a filler material is interposed between the surfacecoating layer and the solar cell. As the filler material, there isgenerally used EVA (ethylene-vinyl acetate copolymer), butyral resin, orthe like. A back surface film is provided on the back surface of theconductive substrate of the solar cell by means of a filler material. Asthe back surface film, there is used a nylon film, a fluororesinlaminated aluminum film, or the like. Moreover, in a practical solarcell module, a reinforcing material is provided on the back surface ofthe back surface film by means of a filler material. Hence, each of thefiller materials interposed between the surface coating layer and thesolar cell and between the conductive substrate and the back surfacefilm must function as an adhesive and while protecting the photovoltaicelement from scratch damage and exterior impacts.

The interior protective ability of the protective means having the aboveconstruction, however, is dependent on the thickness of the coatingmaterial composed of the surface coating layer on the light receivingsurface and the filler material. Specifically, as the thickness of thecoating material is increased, the interior protective ability isincreased; and as it is decreased, the interior protective ability isreduced. However, when the thickness of the surface coating layer on thelight receiving surface side is increased, separation tends to occur atthe interface between the surface coating layer and the filler materialdue to temperature change. The separation causes a problem in thatmoisture reaches the solar cell through the separated portion, andthereby not only the characteristics of the solar cell are reduced butalso a leakage current is generated due to permeation of moisture. Thefiller material which encloses the solar cell must fill theirregularities of the solar cell and adhere to the surface coatinglayer. The filler material is thus required to have a rubber elasticity.

Moreover, as the thickness of the surface coating material is increased,the light transmissivity thereof is reduced, which lowers the conversionefficiency of the solar cell. The solar cell module having the aboveconstruction is generally manufactured in the following procedure.Namely, a resin film as the front surface coating layer on the lightreceiving surface side, a front surface filler material, a solar cell, aback surface filler material, and a back surface film are laminated, andthen hot-pressed using a vacuum laminator. In this manufacturing method,since the end portions of the solar cell module come into close-contactupon hot-pressing, air sometimes remains in part of the interior betweenthe filler material and the surface coating material on the lightreceiving surface side and between the filler material and the solarcell. As a result, bubbles often remain in the sealed solar cell module.The bubbles thus remaining in the solar cell module are repeatedlyexpanded and contracted due to temperature changes, thus leading to theseparation of the coating material. The thus generated separation causesthe above-described problem that moisture reaches the solar cell throughthe separated portion, whereby the conversion efficiency is reduced.Moreover, the remaining bubbles deteriorate the appearance of the solarcell module, thereby reducing the yield of products.

As a means for solving the above-described problem, there is known amethod of inserting unwoven glass fiber fabric between the fillermaterial and the surface coating layer on the light receiving surfaceside and between the filler material and the solar cell, and thenlaminating them. In this method, the surface coating material isreinforced by glass fibers, and it is thus improved in its mechanicalstrength. The interior protective ability of the surface coatingmaterial against an external force is increased because of the increasedmechanical strength, and thereby the thickness of the surface coatingmaterial can be reduced. This makes it possible to prevent the aboveseparation which more readily occurs when the thickness of the surfacecoating layer on the light receiving surface side is large. Moreover,since the thickness of the surface coating material can be relativelythin, the reduction in the light transmissivity of the surface coatingmaterial the reduction in the conversion efficiency of the solar cellare suppressed.

In the manufacturing process of the solar cell module, since glassfibers are interposed between the filler material and the solar cell andbetween the solar cell and the surface coating layer on the lightreceiving surface side, even when the solar cell module is pressed, airvent passages can be ensured at the end portion of the solar cellmodule, thereby facilitating evacuation and elimination of the remainingbubbles.

In this case, however, the glass fibers are inevitably exposed at theend portion of the solar cell module, and thereby moisture easilypermeates into the solar cell module by way of the glass fibers, thepermeating moisture sometimes exerting adverse effects on the solarcell. To prevent the glass fibers from being exposed at the end portionof the solar cell module, there may be considered a method of previouslycutting the glass fibers into sizes smaller than that of the solar cellmodule; however, in this case, the end portion of the solar cell modulewould lack air vent passages similarly to the structure with no glassfibers, thereby generating the bubbles. This method, therefore, fails tosufficiently solve the above-described problem.

SUMMARY OF THE INVENTION

The present inventors have experimentally examined the problems of theabove-described coating materials of the prior art solar cell modules,and have found that the above-described problems of the prior art solarcell module can be solved without glass fibers as in the prior art, bymeans of a method wherein a photovoltaic element (solar cell) isenclosed by a filler material and a surface coating material having amulti-layer structure containing a hard resin layer is disposed on thelight receiving surface side of the photovoltaic element.

The present invention has been accomplished on the basis of theabove-described knowledge.

A principal object of the present invention is to provide an improvedsolar cell module having a surface coating material satisfying therequirements for a solar cell module without glass fibers as used in theprior art, thereby solving the above-described problems of the prior artsolar cell modules.

Another object of the present invention is to provide a solar cellmodule having a surface coating material which excels in weatherability,heat resistance, and adhesion to a photovoltaic element (solar cell),and which has the functions of protecting the photovoltaic element(solar cell) from an exteriorly applied force (external pressure) and ofkeeping the deterioration of the photovoltaic element (solar cell) dueto moisture permeation at a minimum, thereby achieving a desiredconversion efficiency for a long period of time.

A further object of the present invention is to provide an improvedsolar cell module comprising a photovoltaic element (solar cell)enclosed by a filler material and coating material having athree-layered structure disposed on the filler material on the lightreceiving surface side of the photovoltaic element, wherein said coatingmaterial includes a hard resin layer having a hardness of at least 50 inShore hardness D; an adhesive layer having a function of absorbingultraviolet rays with wavelengths which cause deterioration of the hardresin layer and of transmitting ultraviolet rays necessary for powergeneration by the photovoltaic element, and also having an adhesivefunction; and an outermost layer of excellent weatherability (the hardresin layer itself having excellent stability against heat, light, andmoisture), said hard resin layer, adhesive layer, and outermost layerbeing laminated on the filler material on the light receiving side ofthe photovoltaic element in this order, whereby even when an externalforce (external pressure) is applied, the photovoltaic element isstabilized and the surface coating material is excellent inweatherability, heat resistance, and moisture resistance, withoutoccurrence of any separation; and the photovoltaic element is preventedfrom being deteriorated even upon outdoors use for a long period oftime, thus achieving a desired photoelectric conversion efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an example of a solar cellmodule of the present invention;

FIG. 2 is a schematic cross-sectional view of an example of a solar cellelement used in the solar cell module shown in FIG. 1;

FIG. 3 is a schematic illustrative view of the scratch test procedure;

FIG. 4 is a view showing the component members of an example of a solarcell module of the present invention;

FIG. 5 is a view showing the component members of a prior art solar cellmodule; and

FIG. 6 is a view showing the component members of another example of aprior art solar cell module.

DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention solves the above-described problems in the priorart solar cell modules and achieves the above-described objects. A solarcell module of the present invention has the following construction.Namely, the solar cell module comprises a photovoltaic element (solarcell) enclosed by a filler material and an overlying coating materialhaving a three-layered structure disposed on the light receiving surfaceside of the photovoltaic element, wherein said coating element includesa hard resin layer having a hardness of at least 50 in Shore hardness D;an adhesive layer having the functions of absorbing ultraviolet rayswith wavelengths which cause deterioration of the hard resin layer andof transmitting ultraviolet rays necessary for power generation by thephotovoltaic element, and also having an adhesive function; and anoutermost layer having excellent weatherability (the hard resin layeritself having excellent stability against heat, light, and moisture),said hard resin layer, adhesive layer and outermost layer beinglaminated in this order. The coating material having the above-describedthree-layered structure in the solar cell module of the presentinvention provides the following functions: (1) prevents thephotovoltaic element from being damaged due to an externally appliedpressure and hence to protect the solar cell; (2) weatherability, heatresistance, moisture resistance, and scratch resistance necessary forthe solar cell module; (3) ensures adhesion with the photovoltaicelement (solar cell); (4) minimizes deterioration of the photovoltaicelement (solar cell) due to moisture permeation; and (5) provides adesired conversion efficiency of the photovoltaic element for a longperiod of time.

The solar cell module having the above construction according to thepresent invention will now be described in detail.

FIG. 1 is a schematic cross-sectional view of a solar cell module of thepresent invention. In FIG. 1, reference numeral 101 indicates a hardresin layer; 102 is an adhesive layer; 103 is an outermost layer; 104 isa filler material layer; 105 is a photovoltaic element; and 106 is aback surface insulating layer. In the solar cell module shown in FIG. 1,sunlight is impinged through the outermost layer 103, passes through theadhesive layer 102, hard resin layer 101, and filler material layer 104,and reaches the photovoltaic element 105. Electromotive force isgenerated by the photovoltaic element 105.

Each component of the solar cell module of the present invention will bedescribed below.

Hard Resin Layer

The hard resin layer 101 is made of a resin having a hardness of 50 ormore in Shore hardness D. The hard resin layer 101 is required to beexcellent in transparency and to exhibit a strong resistance againstexternal pressure and the like. The hard resin layer is made of highdensity polyethylene (at least 60 in Shore hardness D), polycarbonate(at least 70 in Shore hardness D), polyethylene terephthalate, i.e. apolyester resin (at least 80 in Shore hardness D), polyarylate (at least70 in Shore hardness D) or polyamide resin (at least 70 in Shorehardness D). Specific examples of these resins preferably includepolycarbonate, polyethylene terephthalate as a polyester resin, andpolyarylate. Each of these resins is preferably used in the form of afilm. Of these resins, the polycarbonate film is very high in mechanicalstrength, is poor in weatherability but is difficult to be discolored orreduced in mechanical strength when shielded from ultraviolet rays bythe adhesive layer, with the result that it can be practically used. Inthe case of polyethylene terephthalate, the biaxial orientated filmthereof is preferable because it is very high in mechanical strength andis not torn and pierced by pressure applied from the exterior. Thepolyarylate resin film has a very high heat resisting temperature andthereby it sufficiently withstands operation at a high temperature. Tomaintain the mechanical strength without reduction in transmission, thethickness of the hard resin layer 101 is preferably in the range of from25 to 200 μm, more preferably, in the range of from 75 to 125 μm.

Incidentally, in the hard resin films used for the prior art solar cellmodules, a type is known which contains an ultraviolet absorbent forimproving the weatherability. However, the layer formed of such a hardfilm absorbs light having a wavelength less than about 400 nm, thusreducing the conversion efficiency of the photovoltaic element. In thepresent invention, therefore, such a hard film is not used.

The above-described hard resin film used as the hard resin layer 101 ispreferably subjected to corona discharge treatment, ozonation, or primercoating treatment for ensuring adhesion with the filler material 104 andthe adhesive layer 102.

Adhesive Layer

The adhesive layer 102 is required to exhibit the functions ofprotecting the hard resin layer 101 from ultraviolet rays and oftransmitting sufficient light necessary for photoelectric conversion bythe photovoltaic element. Moreover, it must ensure the adhesive strengthwith the outermost layer 103 and the hard resin layer 101. In the casewhere the photovoltaic element is made of a-Si and has a plurality ofphotoelectric conversion layers, the wavelengths of lightphotoelectrically converted in the respective photoelectric conversionlayers are different from each other. If light necessary for a layerwhich converts light having a short-wavelength into electric power isshielded by the adhesive layer 102, the current generated in thephotoelectric conversion layer is reduced, thus lowering the conversionefficiency of the photovoltaic element. To prevent the reduction in theconversion efficiency of the photovoltaic element, the adhesive layer102 is made of a specified resin film having a total light transmissionwhich is preferably at least 90% for light having a wavelength of 400 nmand above, at least 50% for 380 nm, and up to 10% for 350 nm and below;more preferably, at least 95% for 400 nm and above, at least 80% for 380nm, and less than 5% for 350 nm and below. To realize the required lighttransmission of the adhesive layer, the adhesive layer is formed of anadhesive resin which is mixed with an ultraviolet absorbent in aspecified amount. Moreover, the adhesive layer 102 is required to betransparent to light used for photoelectric conversion. Specificexamples of the resins which satisfy the requirements for the adhesivelayer, include ethylene-vinyl acetate copolymer (EVA), polyvinyl butyral(PVB), silicon resin, and acrylic resin. In the case where the adhesivestrength of the adhesive layer 102 is insufficient, the adhesivestrength can be enhanced by using a silane coupling agent or a titanatecoupling agent. The above adhesive resin constituting the adhesive layer102 preferably contains an ultraviolet absorbent for providing a desiredultraviolet ray shielding function to the adhesive layer. The usableultraviolet absorbents include organic ultraviolet absorbents andinorganic ultraviolet absorbents. As an organic ultraviolet absorbent,there may be preferably used a benzophenyl series, salicylate series,benzotriazole series, or acrylonitrile series ultraviolet absorbent.More preferably, specific examples of the organic ultraviolet absorbentsinclude 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-n-octoxybenzophenone, and2-(2-hydroxy-5-t-octylphenyl)-benzotriazole. Specific preferableexamples of the inorganic ultraviolet absorbents include TiO₂, CeO₂,ZnO, and SnO₂.

Outermost Layer

It is important that the outermost layer 103 be stable against heat,light, and moisture (i.e. excellent in weatherability). Moreover, it isdesirable that the outermost layer prevent reduction in the efficiencyof the photovoltaic element due to contamination. For this purpose, theoutermost layer is desired to be excellent in water repellency. Thewater repellency is preferably 50° or more, more preferably, 70° or morein terms of the contact angle with water. The outermost layer 103 isformed of fluororesin or silicone resin.

In the preferred mode, the outermost layer 103 is formed of fluororesin.Specific examples of the fluororesins includetetrafluoroethylene-ethylene copolymer, trifluoroethylene chlorideresin, tetrafluoroethylene-perfluoroalkyl vinylether copolymer,tetrafluoroethylene-hexafluoropropylene, fluorovinylidene, andfluorovinyl resin. The outermost layer made of such resins is preferablysubjected to corona treatment, ozonation, or primer coating for ensuringstrong adhesion with the adhesive layer 102.

Filler Material Layer

The filler material layer 104 is required to have adhesive strengthbetween the back surface insulating film 106 and the photovoltaicelement 105, and between the photovoltaic element 105 and the hard resinlayer 101. It is essential that the filler material layer bethermoplastic for filling the irregularities on the photovoltaic element105 and giving smoothness to the hard resin layer. The filler materiallayer positioned on the light incident side of the photovoltaic element105 is required to be transparent. The filler material layer 104 is madeof ethylene-vinyl acetate copolymer (EVA), polyvinyl butyral (PVB),silicone resin, epoxy resin, or acrylic resin. The filler material layerpositioned on the back surface may be opaque. The resin used for thefiller material layer may contain a crosslinking agent, thermaloxidation preventive agent, etc. for improving the heat resistance, andalso may contain an ultraviolet absorbent or light oxidation preventiveagent for improving light stability. In the case where the adhesivestrength between the filler material layer and the photovoltaic elementis insufficient, the adhesion can be improved by the addition of asilane coupling agent or titanate coupling agent.

Photovoltaic Element (Solar Cell)

The photovoltaic element 103 of the present invention comprises asemiconductor photoactive layer as a photoelectric conversion memberformed on a conductive substrate. FIG. 2 is a schematic view showing theconstruction of an example of the photovoltaic element. In FIG. 2,reference numeral 201 indicates a conductive substrate, 202 is a backsurface reflection layer, 203 is a semiconductor photoactive layer, 204is a transparent conductive layer, and 205 is a collecting electrode.The conductive substrate 201 functions as the base of the photovoltaicelement (solar cell), and also serves as a lower electrode. Theconductive substrate 201 is composed of silicon, tantalum, molybdenum,tungsten, stainless steel, aluminum, copper, titanium, carbon sheet,lead plated steel plate, or a resin or ceramic film coated with aconductive layer. On the conductive substrate 201, a metal layer, metaloxide layer, or a metal layer and metal oxide layer combination may beformed as the back surface reflection layer 202. In this case, the metallayer can be made of, for example, Ti, Cr, Mo, W, Al, Ag, or Ni. Themetal oxide layer is made of, for example, ZnO, TiO₂, or SnO₂. The metallayer and the metal oxide layer can be formed by resistance heatingevaporation, electron beam evaporation, or sputtering. The semiconductorphotoactive layer 203 is used for photoelectric conversion, and it ismade of a pn-junction polycrystalline silicon, pin-junction amorphoussilicon, or of compound semiconductors such as CuInSe₂, GaAs, Cds/Cu₂ S,CdS/CdTe, CdS/InP, and CdTe/Cu₂ Te. The semiconductor photoactive layer,when composed of polycrystalline silicon, can be formed by a method inwhich molten silicon is molded into a sheet or amorphous silicon isheat-treated. The semiconductor photoactive layer, when composed ofamorphous silicon, is formed by plasma CVD using silane gas as a rawmaterial. The semiconductor photoactive layer, when composed of (a)compound semiconductor(s), is formed by ion plating, ion beamdeposition, vacuum evaporation, sputtering, or electro-deposition. Thetransparent conductive layer 204 serves as an upper electrode of thephotovoltaic element (solar cell). The transparent conductive layer 204is made of, for example, In₂ O₃, SnO₂, In₂ O₃ -SnO₃ -SnO₂ (ITO), ZnO,TiO₂, Cd₂ SnO₄, or a highly doped crystalline semiconductor layer. Thetransparent conductive layer 204 can be formed by resistance heatingevaporation, sputtering, spraying, CVD, or impurity diffusion. Agrid-like collecting electrode 205 may be provided on the transparentconductive layer 204 for effectively collecting the generated current.As specific examples of the material used for the collecting electrode205, there may be used a conductive paste in which a fine powder ofsilver, gold, copper, nickel or carbon is dispersed in a binder polymer.Specific examples of the binder polymers include resins such aspolyester, epoxy, acryl, alkyd, polyvinyl acetate, rubber, urethane, andphenol. In the case of using the above conductive paste, the collectingelectrode is formed by a coating method. Besides this method, thecollecting electrode can be formed by sputtering using a mask pattern,resistance heating, CVD, a patterning method in which a metal film isevaporated over the whole surface and unnecessary portions are removedby etching, a method of directly forming a grid electrode pattern byphoto-CVD, and a method of forming a mask of a negative pattern of agrid electrode pattern, followed by plating. Output terminals 206 aremounted to the conductive substrate and the collecting electrode foroutputting electromotive force. One output terminal is mounted on theconductive substrate by a method wherein a metal body such as a coppertab is joined by spot welding or soldering. The other output terminal iselectrically connected to the collecting electrode electricallyconnected using conductive adhesive or solder 207. In mounting theoutput terminal 206 to the collecting electrode 205, an insulator 208 ispreferably provided for preventing short-circuit due to contact betweenthe output terminal 206 and the conductive substrate 201 andsemiconductor layer 203. A plurality of photovoltaic elements (solarcells) having the above construction are connected in series or inparallel in accordance with a desired voltage or current. A plurality ofthe photovoltaic elements having the above construction can beintegrated on an insulated substrate to obtain a desired voltage orcurrent.

Back Surface Insulating Layer

In the case of a photovoltaic element (solar cell) having a conductivesubstrate, the back surface insulating layer 106 is provided to insulatethe conductive substrate from the outside of the solar cell module. Theback surface insulting layer 106 is formed of a film of nylon,polyethylene, polyester or polystyrene.

Hereinafter, the present invention will be described in detail withreference to examples. In addition, the present invention is not limitedto the examples.

EXAMPLE 1

In this example, a solar cell module having the construction shown inFIG. 1 was prepared.

Referring to FIG. 4, there were prepared a back surface insulating layermember 401, a back surface side filler material member 402, aphotovoltaic element (solar cell) 403, a front surface side fillermaterial member 404, a hard resin layer member 405, an adhesive layermember 406, and an outermost layer member 407. These members 401 to 407were then laminated to prepare the solar cell module of the presentinvention.

As the back surface insulating layer member 401, nylon (trademark name:DARTEK (thickness: 75 μm), produced by Du Pont Company) was used.

Each of the filler material layer members 402 and 404, and the adhesivelayer member 406 was prepared as follows: Namely, 100 parts by weight ofEVA (trademark name: EVAFLEX 150, produced by Mitsui/Du Pont PolyChemical Company), 1.5 parts by weight of a crosslinking agent(trademark name: LUPERSOL, produced by Penwal Company), 0.3 parts byweight of a UV absorbent (trademark name: Cyasorb 531, produced byCyanamid Company), 0.2 parts by weight of an oxidation preventive agent(trademark name: Nowguard P. produced by Uniroyal Company), and 0.1parts by weight of a light stabilizer (trademark name: Chinubin 770,produced by Ciba Geigy Company) were mixed, and the resultant mixturewas extruded by an extruder having a T die, to prepare each member inthe form of a film. The thickness of the film used as the adhesive layermember 406 was 100 μm. The thickness of the film used for each of thefiller material layer members 402 and 406 was 150 μm.

The photovoltaic element 403 having the construction shown in FIG. 2 wasprepared as follows: Namely, a previously cleaned strip-like stainlesssteel substrate 201 was first prepared. On the substrate, an A1 layer(thickness: 5000 Å) and a ZnO layer (thickness: 5000 Å) weresequentially formed as the back surface reflection layer 202 bysputtering. Then, a tandem type a-Si photoelectric conversionsemiconductor layer 203 having a structure comprising an n-layer (filmthickness 150 Å)i-layer (film thickness 4000 Å/p-layer (film thickness100 Å)/n-layer (film thickness 100 Å/i-layer (film thickness 800Å/p-layer (film thickness 100 Å) was prepared by plasma-CVD. In thiscase, the n-type a-Si layer was formed using a mixed gas of SiH₄, PH₃,and H₂ ; the i-type a-Si layer was formed using a mixed gas of SiH₄ andH₂, and a p-type fine crystal μc-Si layer was formed using a mixed gasof SiH₄, BF₃, and H₂. Next, an In₂ O₃ thin film (thickness: 700 Å) asthe transparent conductive layer 204 was formed by a method wherein Inwas evaporated under an O₂ atmosphere by resistance heating. The samplethus obtained was cut into a plurality of elements (size: 30 cm×15 cm).From the plurality of elements, two pieces were selected, each of whichwas formed with a collecting grid electrode 205 by screen printing usingsilver paste (trademark number: #5007, produced by Du Pont Company), tothus obtain a solar cell element. Two of the solar cell elements wereconnected in series by bonding using silver paste (trademark number:#220, produced by Kesuru Company) by way of a copper tab (thickness: 50μm). Moreover, an output terminal from the stainless steel substrate wasmounted using a copper tab (thickness: 50 μm) and silver paste(trademark number: #220 produced by Kesuru Company). Next, a polyamideresin (trademark name: Kapton film (thickness: 50 μm), produced by 3MCompany) was provided ont he element as the insulator 208 as shown inFIG. 2, and another output terminal was connected using a copper tab(thickness: 50 μm) and silver paste (trademark number: #220, produced byKesuru Company). Thus, the photovoltaic elements 403 was prepared.

As the hard resin layer member 405, a polycarbonate film (trademarkname: IUPILON (thickness: 100 μm, hardness: 82 in Shore hardness D,produced by Mitsubishi Gas Chemical Company) was prepared. The bondingsurfaces of the polycarbonate film with the filler material and theadhesive layer were subjected to corona discharge treatment.

As the outermost resin member 407, ETFE fluororesin film (trademarkname: AFLEX (thickness: 50 μm), produced by Asahi Glass Company) wasprepared. The bonding surface of ETFE film with the adhesive layer wassubjected to corona treatment.

On an aluminum plate (thickness: 20 mm) having a heat source, the backsurface insulating layer member 401, back surface side filler materiallayer member 402, photovoltaic element 403, front surface side fillermaterial member 404, hard resin layer member 405, adhesive layer member406, and outermost member 407 were laminated in this order, to obtain alaminated body. A sheet made of heat resisting silicone rubber(thickness: 3 mm) was placed on the laminated body. Subsequently, theinterior of the laminated body was evacuated to a vacuum of 10 mm Hg bya vacuum pump. In this case, an O-ring was used as a sealant. Afterbeing sufficiently evacuated, the laminated body was heated from roomtemperature to 150° C. and held at 150° C. for 20 min. Thus, a solarcell module was obtained. In this way, a plurality of the solar cellmodules was obtained.

The solar cell modules thus obtained were evaluated by the followingprocedure.

Scratch Test

This test was made to examine whether the protective ability of thesurface coating material of the solar cell module against scratchingapplied from the exterior is sufficient. In this test, a steel blade 302was first moved along the surface of the solar cell module in thedirection of the arrow D at a speed of 152.4 mm/sec while a load (F) of4 lbs was applied. A high voltage dielectric breakdown test wasperformed in the following manner after the scratch test, and a standardwas set such that the solar cell modules in which the generated leakagecurrent was less than 50 μA were acceptable. The scratch test wasperformed on the upper outer surface of the tab type connection memberlocated at the highest position in the solar cell module. A high voltagedielectric breakdown test next performed will be described below. Theanode and cathode of the solar cell module were short-circuited afterthe scratch test. The sample thus obtained was dipped in a solutionhaving an electrical conductivity of 3500 ohm·cm containing 0.1 wt % ofTriton X-100 (trademark name) as a surface active agent. At this time,the scratched portion was dipped while the output terminal of the samplewas not dipped in the solution. The cathode of a power source was dippedin the solution and the anode of the power source was connected to theoutput terminal of the sample. The evaluation was performed under thecondition that a voltage of 2000 V was applied. The results obtained areshown in Table 1 in accordance with the following standard: namely, amark ◯ indicates the case where current flow was less than 0.5 μA, and amark X indicates the case where current flow was 0.5 μA or more.

Hail Impact Test

This test is performed to examine the protective ability of the interiorof a solar cell module against external pressure and impacts. This testwas performed in the following procedure: Namely, ten balls of ice, eachhaving a diameter of one inch, are made to collide with each portion ofa solar cell module in which the mechanical strength is weak (the centerof the photovoltaic element, corners of the module, edges, connectionportion of the photovoltaic element) at a speed of 23.2 m/sec. The solarcell module thus tested was visually evaluated in terms of the presenceor absence of layer separation and cracking, and in terms ofphotoelectric conversion efficiency. The evaluation of the photoelectricconversion efficiency was performed by a method wherein thephotoelectric conversion efficiencies before and after the Hail impacttest were measured, and the ratio of change therebetween was examined.The results obtained are shown in Table 1 in accordance with thefollowing standard; namely, a mark ⊚ indicates the case where layerseparation and cracking are not observed at all, and the change ratio isless than 5%, a mark ◯ indicates the case where a slight amount of layerseparation and cracking are observed but the change ratio is less than5%, and a mark X indicates the case where layer separation and crackingare frequently observed and the change ratio is 5% or more.

Adhesive Force in High Temperature/High Moisture

A solar cell module was held for 100 hours in the condition of 85°C./85% (relative moisture), and the adhesive strength of the solar cellmodule at the end portion of the coating material was qualitativelyevaluated in the condition of 85° C./85% (relative moisture) by acrossing-type separation method. The results obtained are shown in Table1 in accordance with the following standard: namely, a mark ⊚ indicatesthe case where the adhesive strength is excellent, a mark ◯ indicatesthe case where the adhesive strength is sufficient to be practicallyused, and a mark X indicates the case where the adhesive strength isinsufficient.

Weatherability

A solar cell module was subjected to an accelerated weatherability test.Specifically, the solar cell module was placed in a sunshine weathermeter and was subjected to a light irradiation and raindrop cycle for5000 hours, after which it was evaluated in terms of the appearancechange and photoelectric conversion efficiency. The appearance changewas visually evaluated, and the results obtained are shown in Table 1 inaccordance with the following standard: namely, a mark ⊚ indicates thecase where no appearance change is observed, a mark ◯ indicates the casewhere a slight appearance change is observed but is sufficient to bepractically used, and a mark X indicates the case where the appearanceis insufficient to permit practical use because layer separation,cracking, and discoloring are observed.

The photoelectric conversion efficiency was evaluated by a methodwherein the photoelectric conversion efficiency of the solar cell modulewas measured after testing, and the measured value was compared with thephotoelectric conversion efficiency before testing (this was taken as1), to obtain a relative value. Accordingly, the value shown in Table 1is the relative value. In addition, the deterioration of the amorphoussilicon photovoltaic element itself was omitted.

Durability Against Temperature Change

The solar cell module was subjected to a testing cycle (-40° C./onehour: 85° C./one hour) conducted 50 times, and the appearance of thesolar cell module was visually evaluated. The results obtained are shownin Table 1 in accordance with the following standard: namely, a mark ⊚indicates the case where no appearance change is observed, a mark ◯indicates the case where a slight appearance change is observed, a mark◯ indicates the case where a slight appearance change is observed butthe module is practically usable, and a mark X indicates the case wherethe appearance is insufficient because layer separation, cracking, anddiscoloring are observed to an extent which reduces module reliability.

EXAMPLE 2

A plurality of solar cell modules were obtained by the same procedure asin Example 1, except that the resin used for the hard resin layer member405 was replaced with a polyethylene terephthalate film (trademark name:LUMIRROR, thickness: 50 μm, hardness: 90 in Shore hardness D, producedby TORAY INDUSTRIES).

The solar cell modules thus obtained were evaluated by the sameprocedure as in Example 1. The results obtained are shown in Table 1.

EXAMPLE 3

A plurality of solar cell modules were obtained by the same procedure asin Example 1, except that the resin used for the hard resin layer member405 was replaced with a polyarylate film (trademark name: EMBLATE,thickness: 100 μm, hardness: 77 in Shore hardness D, produced byUNITIKA).

The solar cell modules thus obtained were evaluated by the sameprocedure as in Example 1. The results obtained are shown in Table 1.

EXAMPLE 4

A plurality of solar cell modules were obtained by the same procedure asin Example 1, except that the resin used for the adhesive layer member406 was replaced with a butyral resin.

The solar cell modules thus obtained were evaluated by the sameprocedure as in Example 1. The results obtained are shown in Table 1.

EXAMPLE 5

A plurality of solar cell modules were obtained by the same procedure asin Example 1, except that the resin used for the adhesive layer member406 was replaced with methylbutyl methacrylate copolymer.

The solar cell modules thus obtained were evaluated by the sameprocedure as in Example 1. The results obtained are shown in Table 1.

COMPARATIVE EXAMPLE 1

First, there were prepared a back surface insulating layer member 501, aback surface side filler material member 502, a photovoltaic element(solar cell) 503, a front surface side filler material member 504 and anoutermost layer member 505. These members were then laminated as shownin FIG. 5 using the same procedure as in Example 1.

The back surface insulating layer member 501, back surface side fillermaterial member 502, photovoltaic element (solar cell) 503, andoutermost layer member 505 were the same as those in Example 1. Thefront surface side filler material member 504 was prepared by the sameprocedure as in Example 1, except that the thickness was changed to 350μm. A plurality of solar cells were obtained.

The solar cell modules thus obtained were evaluated by the sameprocedure in Example 1. The results obtained are shown in Table 1.

COMPARATIVE EXAMPLE 2

A plurality of solar cell modules were obtained by the same procedure asin Comparative Example 1, except that the thickness of the outermostlayer member 505 was changed to 100 μm.

The solar cell modules thus obtained were evaluated by the sameprocedure in Example 1. The results obtained are shown in Table 1.

COMPARATIVE EXAMPLE 3

First, there were prepared a back surface insulating layer member 601, aback surface side filler material member 602, a photovoltaic element(solar cell) 603, a glass fiber reinforced member 604, a front surfaceside filler material member 605, a glass fiber reinforced member 606,and an outermost layer member 607. These members were then laminated asshown in FIG. 6 using the same procedure as in Example 1, to prepare asolar cell module.

The back surface insulating layer member 601, back surface side fillermaterial member 602, photovoltaic element (solar cell) 603, andoutermost layer member 607 were the same as those in Example 1. Thefront surface side filler material member 604 was prepared by the sameprocedure as in Example 1, except that the thickness was changed to 350μm. As each of the glass fiber reinforced members 604 and 606, unwovenglass fiber fabric (trademark name: Crane Glass 230, produced by CraneGlass Company) was used. A plurality of solar cell modules wereobtained.

The solar cell modules thus obtained were evaluated by the sameprocedure as in Example 1. The results obtained are shown in Table 1.

As is apparent from Table 1, in the solar cell modules of the presentinvention, when any external force is applied, the photovoltaic elementis stable and the surface coating material is excellent inweatherability, heat resistance, and moisture resistance, without anylayer separation; and the photovoltaic element resists deteriorationeven upon outdoor use for a long period of time, thus achieving adesired photoelectric conversion efficiency.

Specifically, the solar cell module of the present invention comprises aphotovoltaic element (solar cell) enclosed by a filler material and acoating material having a three-layered structure which is disposed onthe filler material on the light receiving side of the photovoltaicelement, where said coating element includes a hard resin layer having ahardness of 50 or more in Shore hardness D; and adhesive layer havingthe functions of absorbing ultraviolet rays of wavelengths whichdeteriorate said hard resin layer and of transmitting ultraviolet raysnecessary for electric power generation by the photovoltaic element, andalso having a layer adhesive function; and an outermost layer ofexcellent weatherability (the resin itself having excellent stabilityagainst heat, light, and moisture), said hard resin layer, adhesivelayer, and outermost layer being laminated on the filler material layerin this order. The inventive solar cell module, therefore, can attainthe following effects: (1) prevent the photovoltaic element from beingdamaged by externally applied pressure and hence protecting the solarcell; (2) providing satisfactory weatherability, heat resistance,moisture resistance, and scratch resistance necessary for the solar cellmodule; (3) ensuring adhesion with the photovoltaic element (solarcell); (4) minimizing deterioration of the photovoltaic element (solarcell) due to moisture permeation; and (5) providing a desired conversionefficiency of the photovoltaic element for a long period of time.

                                      TABLE 1                                     __________________________________________________________________________                    adhesive strength  durability                                             Hail                                                                              in high weatherability                                                                           against                                                impact                                                                            temperature/high                                                                            conversion                                                                         temperature                                scratch test                                                                              test                                                                              moisture                                                                              appearance                                                                          efficiency                                                                         change                                     __________________________________________________________________________    Example 1                                                                           ∘                                                                       ⊚                                                                  ⊚                                                                      ⊚                                                                    0.99 ⊚                           Example 2                                                                           ∘                                                                       ⊚                                                                  ⊚                                                                      ⊚                                                                    0.98 ⊚                           Example 3                                                                           ∘                                                                       ⊚                                                                  ⊚                                                                      ⊚                                                                    0.99 ⊚                           Example 4                                                                           ∘                                                                       ⊚                                                                  ∘                                                                         ⊚                                                                    0.98 ⊚                           Example 5                                                                           ∘                                                                       ⊚                                                                  ⊚                                                                      ⊚                                                                    0.99 ∘                              Comparative                                                                         x     x   ∘                                                                         ∘                                                                       0.95 ∘                              Example 1                                                                     Comparative                                                                         ∘                                                                       x   ∘                                                                         ∘                                                                       0.95 x                                          Example 2                                                                     Comparative                                                                         ∘                                                                       ∘                                                                     ∘                                                                         ∘                                                                       0.96 ∘                              Example 3                                                                     __________________________________________________________________________

What is claimed is:
 1. A solar cell module comprising a photovoltaic element having a photoactive semiconductor layer as a light conversion member, said photovoltaic element being enclosed by a filler material, wherein a three-layered coating material comprising a hard resin layer, an adhesive layer and an outermost layer is laminated in this order over the filler material on the light receiving surface side of said photovoltaic element.
 2. A solar cell module according to claim 1, wherein said hard resin layer comprises a resin having a hardness of at least 50 in Shore hardness D.
 3. A solar cell module according to claims 1 or 2, wherein said hard resin layer is selected from polycarbonate resin and polyester resin.
 4. A solar cell module according to any of claims 1 or 2, wherein the thickness of said hard resin layer is in the range of from 50 to 125 μm.
 5. A solar cell module according to any of claims 1 or 2, wherein said adhesive layer comprises a thermoplastic resin containing an ultraviolet absorbent.
 6. A solar cell module according to claim 5, wherein said adhesive layer has a total light transmissivity which is at least 90% for light having a wavelength of 400 nm and above; at least 50% for 380 nm, and up to 10% for 350 nm and below.
 7. A solar cell module according to claim 5, wherein the thermoplastic resin of said adhesive layer is selected from ethylene-vinyl acetate copolymer (EVA), polyvinyl butyral (PVB), silicone resin, and acrylic resin.
 8. A solar cell module according to any of claims 1 or 2, wherein the thickness of said adhesive layer is in the range of from 50 to 200 μm.
 9. A solar cell module according to any of claims 1 or 2, wherein said outermost layer comprises a resin having an aqueous contact angle of 70° and above.
 10. A solar cell module according to claim 9, wherein said outermost layer comprises a fluororesin.
 11. A solar cell module according to any of claims 1 or 2, wherein said semiconductor photoactive layer is an amorphous semiconductor thin film.
 12. A solar cell module according to claim 11, wherein said amorphous semiconductor thin film comprises amorphous silicon.
 13. A solar cell module according to claim 1, wherein the filler material is selected from the group consisting of ethylene-vinyl acetate copolymer (EVA), polyvinyl butyral (PVB), silicone resin, epoxy resin, and acrylic resin.
 14. A solar cell module according to claim 1, wherein the filler material contains one or more materials selected from the group consisting of a crosslinking agent, an antioxidant, and an ultraviolet absorbent.
 15. A solar cell module according to claim 1, wherein the photovoltaic element comprises a substrate, an aluminum layer disposed on said substrate, a zinc oxide layer disposed on said aluminum layer, a photoactive semiconductor layer disposed on said zinc oxide layer, and a transparent conductive layer disposed on said photoactive semiconductor layer.
 16. A solar cell module according to claim 15, wherein the photoactive semiconductor layer comprises a laminate of an n-type semiconductor layer, an i-type semiconductor layer, and a p-type semiconductor layer.
 17. A solar cell module according to claim 16, wherein the p-type semiconductor layer contains a microcrystalline silicon material.
 18. A solar cell module according to claim 16, wherein the i-type semiconductor layer contains an amorphous silicon material.
 19. A solar cell module according to claim 16, wherein the n-type semiconductor layer contains an amorphous silicon material.
 20. A solar cell module according to claim 15, wherein the photoactive semiconductor layer comprises a plurality of stacked bodies, each comprising a laminate of an n-type semiconductor layer, an i-type semiconductor layer, and a p-type semiconductor layer.
 21. A solar cell module according to claim 20, wherein the p-type semiconductor layer contains a microcrystalline silicon material.
 22. A solar cell module according to claim 20, wherein the i-type semiconductor layer contains an amorphous silicon material.
 23. A solar cell module according to claim 20, wherein the n-type semiconductor layer contains an amorphous silicon material.
 24. A solar cell module according to claim 15, wherein the photoactive semiconductor layer comprises two stacked bodies each comprising a laminate of an n-type semiconductor layer, an i-type semiconductor layer, and a p-type semiconductor layer.
 25. A solar cell module according to claim 24, wherein the p-type semiconductor layer contains a microcrystalline silicon material.
 26. A solar cell module according to claim 24, herein the i-type semiconductor layer contains an amorphous silicon material.
 27. A solar cell module according to claim 24, wherein the n-type semiconductor layer contains an amorphous silicon material.
 28. A solar cell module according to claim 15, wherein a collecting electrode is disposed on the transparent conductive layer.
 29. A solar cell module according to claim 1, which further comprises an insulating member disposed on a side of the photovoltaic element opposite the light receiving surface side.
 30. A solar cell module according to claim 29, wherein the insulating member is a film of nylon, polyethylene, polyester, or polystyrene. 